The rotary Stirling cycle engine system is similar to previously disclosed rotary closed cycle power systems, with large lateral tubing loops located between the hot and cold sources.
This present engine system is nearly identical to previous rotary closed parallel cycle engine system with the exception of the sealing of the rotary units and external tubing loop configurations. The parallel or independent heat transfer tubing arrangement is an improvement over the series gas flow design, when a positive displacement return pump is placed between the two lateral tubing loop groups.
The addition of the rotary return pump insures that the expanding gas in the hot section is kept under pressure and forced into the rotary engine unit, while a suction is created within the the cooling tubing loops and aids in the evacuation of the spent gas within the "cold" engine half. The rotary pump -- is driven by a takeoff belt drive from the rotary engine units and must be a low inertia type to minimize the power drain from the system.
The major difference within the rotary engine units previously disclosed and in this design is that the multiple vanes were not sealed, but revolved at a close clearance to the cylinder bore and side walls of each rotary engine unit. Without sealing the rotary closed cycle engine operates closer to the closed Brayton (turbine) cycle with high gas flow rates, and a lower compression ratio.
The present Stirling cycle engine system with sealed vanes operates at higher compression ratio and lower gas flow velocity than all non-contacting vane engines, and will produce greater torque per BTU input for equivalent sized engines. The rotary Stirling cycle engine is a more desirable gaseous power source becuse of the lower gas flow rates which allow more effective heat transfer for both the hot and cold sources.
When considered from another standpoint, the rotary Stirling will allow shorter heat transfer loops and therefore greater compactness than an equivalent Brayton closed cycle power source.
An important difference in the rotary engine units in this present engine design is the addition of small sleeve (oilite) rollers within the rotors, adjacent to each vane slot. These small rollers secured to the inside side faces of the rotor prevent the vanes from rubbing on the edge surfaces of each slot, so that friction at these points is reduced.
This lower friction, when combined with lower sliding friction of the vane guidance rings result in a closed cycle rotary engine unit of high efficiency and long operating life.
The problem of regeneration within a rotary Stirling engine has been a difficult one to resolve in the past, and it has not been possible to achieve the effectiveness of reciprocating regeneration of the piston type Stirling engine. It is now believed that the effectiveness of reciprocating regeneration can be approached for the rotary version by a combination of internal bypass regeneration and by external heat collection and return regeneration techniques.
Hydrogen, or possibly helium, will be the internal working medium for the rotary engine system which have been successfully used in the piston type of Stirling cycle engine. Hydrogen gas may also be used as the external fuel source, although any type of fuel for the heat source may be employed.